Method of thin strip casting

ABSTRACT

A method for making alloy strip by continuous casting with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%. Molten metal is introduced forming a casting pool supported on the casting rolls and counter-rotating the A heat flux is provided with a peak heat flux &gt;20 Mw/m2. The strip is cooled at 1000-3000 K/sec. A roll biasing force &gt;40 kN/meter of casting roll length is applied to form thin metal strip. The strip is then conveyed through a first enclosure with an atmosphere having an oxygen content of &lt;5%. The cast strip is rolled through a rolling mill and reduced and modification of the microstructure is initiated.

BACKGROUND AND SUMMARY

This invention relates to making thin strip and more particularly casting of thin strip by a twin roll caster.

It is known to cast metal strip by continuous casting in a twin roll caster. Molten metal is introduced between a pair of counter-rotating laterally positioned casting rolls with a nip there between, which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between the rolls to produce solidified strip product delivered downwardly from the nip between the rolls. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel, or tundish, from which it flows through a transition piece to a metal delivery nozzle positioned above the nip, longitudinally between the casting rolls, which delivers the molten metal to the region above the nip to form a casting pool of molten metal. The casting pool of molten metal is supported on the casting surfaces of the rolls above the nip. The casting pool is typically confined at the ends of the casting rolls by side plates or dams held in sliding engagement adjacent the ends of the casting rolls.

In casting thin strip by twin roll casting, the metal delivery nozzles receive molten metal from the moveable tundish through the transition piece and delivers the molten metal in the casting pool in a desired flow pattern. As the casting rolls rotate, metal from the casting pool solidifies into shells on the casting rolls and the shells are brought close together at the nip to produce a solidified cast strip below the nip. The gap between the casting rolls maintains separation between the solidified shells at the nip with semi-solid metal present in the space between the shells at the nip, so that at least part of the strip between the shells is subsequently solidified below the nip. The mushy or semi-solid center portion is thus “swallowed” between the shells and solidified downstream of the nip as the thin strip is cooled. The thickness of the shells and indirectly the thickness of the mush center portion is therefore determined and controlled by the amount of heat flux transferred from the shells to the casting rolls as the shells are formed in moving through the casting pool. In the past, these parameters limited the steel compositions that could be cast into thin strip by twin roll caster to those with freezing range (i.e. temperature between the liquidus temperature and the solidus temperature) less than 100° C. and typically less than 50° C.

A related concern has been the biasing forces that could be exerted on the thin strip at the nip by the casting rolls. The biasing forces exerted by the casting rolls were limited to those that could maintain the cast shells (with a mushy center portion) as a cast strip with sufficient strength to maintain itself. Again this parameter limited the compositions of steel that could be cast in the twin roll caster to those with a freezing range less than 100° C. and typically less than 50° C.

Another limitation in the past on casting thin strip by the twin roll caster was cooling the cast strip immediately after casting in an enclosure, where oxygen levels were limited to inhibit the formation of scale as the thin strip during cooling. At the same time, the just casted thin strip had to be fed onto a roller table to pinch rolls to exiting the enclosure for downstream processing. This transition had been previously done by a moveable apron that swung up into the strip path moving downward from the nip to feed the strip laterally onto the roller table to the pinch rolls, and when the apron was swung back out of the path of the thin strip following initial feeding the strip to the pinch rolls, a loop was provided through which the thin strip traveled from the casting rolls to the roller table. The strip had to be maintained within a certain level of strain so that the strip did not break at the loop during the casting. This feature again limited the steel compositions that could be cast into thin strip by twin roll caster to those with a freezing range less than 100° C. and typically less than 50° C.

There is therefore a need for development of twin roll casting methods and casting equipment to be able to cast previously known and new steel compositions that have a freezing range greater than 50° C. and preferable greater than 100° C. and that are high in both tensile strength and percent elongation to overcome the previously mentioned limitations.

Currently disclosed is a method for making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting. The method of casting the alloy strip comprises the steps of: assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between; introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C.; providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls; applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip; conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% or not more than 0.2% to form a continuous thin steel strip; and rolling the cast strip through a rolling mill to impart between 10% and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.

Alternatively, a method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15% is produced by continuous casting which comprises assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between; introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C.; providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls; applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% or not more than 0.2%; and heating post cast strip to at least 70% of the melting point of the alloy forming the strip to modify the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.

Further, a method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting comprising:

assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between,

introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula:

R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z),

Where R is one of iron, cobalt or nickel,

-   -   R′ is one or two iron of iron, cobalt or nickel other than R,     -   Cr, B, P, C, and Si respectively represent chromium, boron,         phosphorus, carbon and silicon,     -   M is one or more of molybdenum, vanadium, niobium, titanium,         aluminum, tin, manganese and copper,     -   u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B         and (P, C, Si), respectively, and having the following values:     -   u=30-85     -   v=0-30     -   w=0-45     -   x=0-30     -   y=0-12     -   z=0-7.5         with the provisions that (1) the sum of v+w+x is at least 5, (2)         when x is larger than 20, then w must be less than 20, (3) the         amount of each of vanadium, manganese, copper, tin, magnesium         may not exceed 10 atom percent, and (4) the combined amount of         boron, phosphorus, carbon and silicon may not exceed 13 atom         percent.

providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls,

applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip,

conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.2% to form a thin steel strip, and

rolling the cast strip through a rolling mill to impart between 10 and 40% reduction or heating the post cast strip to at least 70% of the melting point of the alloy forming the strip initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.

These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the disclosed method and are referred to as the following more detailed description of the disclosed method proceeds:

FIG. 1 is a diagrammatical side view of a portion of twin roll caster system for practicing the disclosed method;

FIG. 1A is a diagrammatical view of a portion of twin roll caster for practicing the disclosed method in accordance with an embodiment of the present invention;

FIG. 2 is a partial sectional view through the casting rolls mounted in a roll cassette in the casting position of the caster system of FIG. 1;

FIG. 3 is diagrammatical plan view of the roll cassette of FIG. 2 removed from the caster system;

FIG. 4 is a transverse partial sectional view through the portion marked 4-4 in FIG. 3;

FIG. 5 is an enlarged view of marked detail 5 in FIG. 4;

FIG. 6 is a cross-section of a cast steel strip made as described herein, in accordance with an embodiment of the present invention;

FIG. 7A is a cross-section of a cast steel strip as illustrated in FIG. 6; and

FIG. 7B is an enlarged view of marked detail A in FIG. 7A.

DETAILED DESCRIPTION OF THE DRAWINGS

The embodiments are described with reference to a twin roll caster shown in FIGS. 1 through 5. Referring now to FIGS. 1 and 2, a twin roll caster is illustrated that comprises a main machine frame 10 that stands up from the factory floor and supports a pair of casting rolls mounted in a module in a roll cassette 11. The casting rolls 12 are mounted in the roll cassette 11 for ease of operation and movement as described below. The roll cassette facilitates rapid movement of the casting rolls ready for casting from a setup position into an operative casting position in the caster as a unit, and ready removal of the casting rolls from the casting position when the casting rolls are to be replaced. There is no particular configuration of the roll cassette that is desired, so long as it performs that function of facilitating movement and positioning of the casting rolls as described herein.

The casting apparatus for continuously casting of thin alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30%, with tensile strength of at least 1200 MPa and total elongation of at least 20%, or with tensile strength of at least 1500 MPa and total elongation of at least 15% includes a pair of counter-rotatable casting rolls 12 having shafts 22 (FIG. 3) and casting surfaces 12A laterally positioned to form a nip 18 there between. Molten metal with a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., is supplied from a ladle 13 through a metal delivery system to a metal delivery nozzle 17, core nozzle, positioned between the casting rolls 12 above the nip 18. Molten metal thus delivered forms a casting pool 19 of molten metal above the nip supported on the casting surfaces 12A of the casting rolls 12. This casting pool 19 is confined in the casting area at the ends of the casting rolls 12 by a pair of side closure plates, or side dams 20, (shown in dotted line in FIG. 2). The upper surface of the casting pool 19 (generally referred to as the “meniscus” level) may rise above the lower end of the delivery nozzle 17 so that the lower end of the delivery nozzle is immersed within the casting pool. The casting area includes the addition of a protective atmosphere above the casting pool 19 to inhibit oxidation of the molten metal in the casting area.

The ladle 13 typically is of a conventional construction supported on a rotating turret 40. For metal delivery, the ladle 13 is positioned over a movable tundish 14 in the casting position to fill the tundish with molten metal. The movable tundish 14 may be positioned on a tundish car 66 capable of transferring the tundish from a heating station (not shown), where the tundish is heated to near a casting temperature, to the casting position. A tundish guide, such as rails, may be positioned beneath the tundish car 66 to enable moving the movable tundish 14 from the heating station to the casting position.

The movable tundish 14 may be fitted with a slide gate 25, actuable by a servo mechanism, to allow molten metal to flow from the tundish 14 through the slide gate 25, and then through a refractory outlet shroud 15 to a transition piece or distributor 16 in the casting position. From the distributor 16, the molten metal flows to the delivery nozzle 17 positioned between the casting rolls 12 above the nip 18.

The casting rolls 12 are internally water cooled so that as the casting rolls 12 are counter-rotated, shells solidify on the casting surfaces 12A as the casting surfaces move into contact with and through the casting pool 19 with each revolution of the casting rolls 12. The shells are brought close together at the nip 18 between the casting rolls to produce a thin cast strip product 21 delivered downwardly from the nip. The gap between the casting rolls is such as to maintain separation between the solidified shells at the nip so that mushy metal is present in the space between the shells through the nip, and is, at least in part, subsequently solidified between the solidified shells within the cast strip below the nip.

It is important to achieve rapid cooling of the molten metal over the casting surfaces of the rolls in order to form solidified shells in the short period of exposure on the casting surfaces to the molten metal casting pool during each revolution of the casting rolls. Moreover, it is important to achieve even solidification so as to avoid distortion of the solidifying shells which come together at the nip to form the steel strip. The present method involves a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls. The heat flux between the molten metal and the casting surfaces of the casting rolls may be initially measured and continually measured by methods as described in U.S. Pat. No. 7,299,857. Although this is one way for measuring the heat flux, the heat flux can be measured by any available method.

As shown in FIG. 6, the alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30%, with tensile strength of at least 1200 MPa and total elongation of at least 20%, or with tensile strength of at least 1500 MPa and total elongation of at least 15% made in accordance the present invention may have an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions. These microstructures are illustrated in FIGS. 7A and 7B, where FIG. 7B is an enlarged view of marked detail A in FIG. 7A.

The casting rolls should be set to an appropriate separation or gap of the casting rolls at the nip to allow the casting rolls to move against the action of biasing force to enable the rolls to move to accommodate fluctuations in casting roll separation and strip thickness. The casting roll separation force or biasing force may be used to control the characteristics of the strip. Significant amount of reheating occurs below the roll nip due to the presence of mushy material. The greater the amount of mushy material or the wider the mushy center portion, the longer the strip remains hot. The amount of mushy material between the shells below the nip is controlled by applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip. The bias force restricts the amount of mushy material in the center portion between the shells of the strip allowing the strip to cool sufficiently so there is no effective strength transited in conjunction with the strain on the strip in the loop in the enclosure immediately following casting and the strain is not more than 0.4% or 0.2%, as explained below.

When the amount of mushy material in the center portion between the shells is limited by the biasing force, the temperature of the strip near the edges can be increased relative to the center portion of the strip width. In one embodiment, the crown of the casting rolls may be shaped such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature that the strip in the center portion of the strip width. The crown shape of the casting rolls 12 in combination with the casting roll biasing force is capable of forming the cast strip with mushy metal between the shells so that the cast strip within 25 millimeters of the edge of the strip have a higher temperature that the strip in the center portion of the strip width.

Once the strip exists the nip, the formed cast strip is delivered downwardly from the nip of the casting rolls into a first enclosure containing a protective atmosphere where the strip commences a cooling process after leaving the nip. The strip typically hangs in the enclosure in a loop before moving over a roller table through a first pinch rolls. The disclosed method provides for the thin strip to withstand the transition from the first enclosure to the roller table without breaking. Below the twin roll caster, the cast strip passes through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip. The loop in the enclosure may be between 2.8 and 3 meters.

Alternatively, below the twin roll caster, the cast strip may pass through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.2% to form a thin steel strip. The loop in the enclosure may be between 2.8 and 3 meters.

After exiting the first enclosure, the strip may pass through further sealed enclosures after the pinch roll stand, which may include a hot rolling mill as shown in FIG. 1. FIG. 1 shows the twin roll caster producing the thin cast strip 21, and passing across guide table 30 to pinch roll stand 31 having pinch rolls 31A. Upon exiting the pinch roll stand 31, the thin cast strip may pass through a hot rolling mill 32, comprising a pair of work rolls 32A, and backup rolls 32B, forming a gap capable of hot rolling the cast strip delivered from the casting roll. In the rolling mill 32, the cast strip may be hot rolled to reduce the strip to a desired thickness, improve the strip surface, improve the strip flatness and inducing enough strain to cause modification of the microstructure of the strip. Moreover, the cast strip in hot rolled can have imparted between 10 and 40% reduction initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%. The work rolls 32A have work surfaces providing the desired strip profile across the work rolls.

Alternatively, as shown in FIG. 1A, instead of hot rolling the strip in rolling mill 32, the casted strip may be subject to heating by induction heating 200, or other form of heat as to desired, post casting to heat the strip to at least 70% of the melting point of the alloy forming the strip to modify the microstructure of the cast strip and provide strip with of at least 900 MPa tensile strength and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%. Note that the strip may be cooled after casting and before proceeding with this heating step.

In either embodiment, the cast strip then passes onto a run-out table 33, where it may be cooled by contact with a coolant, such as water, supplied via water jets 90 or other suitable means, and by convection and radiation. In any event, the cast strip may then pass through a second pinch roll stand 91 having rollers 91A to provide tension of the cast strip, and then to a coiler 92. The thin strip may be typically between about 0.3 and 2.0 millimeters in thickness on coiling.

At the start of the casting operation, a short length of imperfect strip is typically produced as casting conditions stabilize. After continuous casting is established, the casting rolls are moved apart slightly and then brought together again to cause this leading end of the cast strip to break away forming a clean head end of the following cast strip. The imperfect material drops into a scrap receptacle 26, which is movable on a scrap receptacle guide. The scrap receptacle 26 is located in a scrap receiving position beneath the caster and forms part of a sealed enclosure 27 as described below. The enclosure 27 is typically water cooled. At this time, a water-cooled apron 28 that normally hangs downwardly from a pivot 29 to one side in the enclosure 27 is swung into position to guide the clean end of the cast strip 21 onto the guide table 30 that feeds it to the pinch roll stand 31. The apron 28 is then retracted back to its hanging position to allow the cast strip 21 to hang in a loop beneath the casting rolls in enclosure 27 before it passes to the guide table 30 where it engages a succession of guide rollers.

An overflow container 38 may be provided beneath the movable tundish 14 to receive molten material that may spill from the tundish. As shown in FIG. 1, the overflow container 38 may be movable on rails 39 or another guide such that the overflow container 38 may be placed beneath the movable tundish 14 as desired in casting locations. Additionally, an overflow container may be provided for the distributor 16 adjacent the distributor (not shown).

The sealed enclosure 27 is formed by a number of separate wall sections that fit together at various seal connections to form a continuous enclosure wall that permits control of the atmosphere within the enclosure. Additionally, the scrap receptacle 26 may be capable of attaching with the enclosure 27 so that the enclosure is capable of supporting a protective atmosphere immediately beneath the casting rolls 12 in the casting position. The enclosure 27 includes an opening in the lower portion of the enclosure, lower enclosure portion 44, providing an outlet for scrap to pass from the enclosure 27 into the scrap receptacle 26 in the scrap receiving position. The lower enclosure portion 44 may extend downwardly as a part of the enclosure 27, the opening being positioned above the scrap receptacle 26 in the scrap receiving position. As used in the specification and claims herein, “seal,” “sealed,” “sealing,” and “sealingly” in reference to the scrap receptacle 26, enclosure 27, and related features may not be a complete seal so as to prevent leakage, but rather is usually less than a perfect seal as appropriate to allow control and support of the atmosphere within the enclosure as desired with some tolerable leakage.

A rim portion 45 may surround the opening of the lower enclosure portion 44 and may be movably positioned above the scrap receptacle, capable of sealingly engaging and/or attaching to the scrap receptacle 26 in the scrap receiving position. The rim portion 45 may be movable between a sealing position in which the rim portion engages the scrap receptacle, and a clearance position in which the rim portion 45 is disengaged from the scrap receptacle. Alternately, the caster or the scrap receptacle may include a lifting mechanism to raise the scrap receptacle into sealing engagement with the rim portion 45 of the enclosure, and then lower the scrap receptacle into the clearance position. When sealed, the enclosure 27 and scrap receptacle 26 are filled with a desired gas, such as nitrogen, to reduce the amount of oxygen in the enclosure and provide a protective atmosphere for the cast strip.

The enclosure 27 may include an upper collar portion 27A supporting a protective atmosphere immediately beneath the casting rolls in the casting position. When the casting rolls 12 are in the casting position, the upper collar portion is moved to the extended position closing the space between a housing portion adjacent the casting rolls 12, as shown in FIG. 2, and the enclosure 27. The upper collar portion may be provided within or adjacent the enclosure 27 and adjacent the casting rolls, and may be moved by a plurality of actuators (not shown) such as servo-mechanisms, hydraulic mechanisms, pneumatic mechanisms, and rotating actuators.

As shown in FIGS. 2-3, cleaning brushes 36 are disposed adjacent the pair of casting rolls 12, such that the periphery of the cleaning brushes 36 may be brought into contact with the casting surfaces 12A of the casting rolls 12 to clean oxides from the casting surfaces during casting. The cleaning brushes 36 are positioned at opposite sides of the casting area adjacent the casting rolls 12, between the nip 18 and the casting area where the casting rolls enter the protective atmosphere in contact with the molten metal casting pool 19.

The side dams 20 may be mounted on and actuated by plate holders 100 positioned one at each end of the roll assembly and moveable toward and away from one another. The plate holders 100 and side dams 20 may be positioned on a core nozzle plate 106 mounted on the roll cassette 11 so as to extend horizontally above the casting rolls, as shown in FIG. 3. The core nozzle plate 106 is positioned beneath the distributor 16 in the casting position and has a central opening 107 to receive the metal delivery nozzle 17. The metal delivery nozzle 17 may be provided in two or more segments, and at least a portion of each metal delivery nozzle 17 segment may be supported by the core nozzle plate 106. The outer end of each metal delivery nozzle 17 is supported by a bridge portion (not shown) positioned adjacent the side dams 20 and capable of supporting and moving the delivery nozzle 17 during casting.

There is shown in FIG. 4 a pair of delivery nozzles 17 formed as substantially identical segments made of a refractory material such as zirconia graphite, alumina graphite or any other suitable material. It must be understood that more than two delivery nozzles 17 may be used in any different sizes and shapes if desired. The delivery nozzles 17 need not be substantially identical in size and shape, although generally such is desirable to facilitate fabrication and installation. Two delivery nozzles 17 may be provided, each capable of moving independently of the other above the casting rolls 12.

Typically where two delivery nozzles 17 are used, the nozzles 17 are disposed and supported in end-to-end relationship as shown in FIG. 4 along the nip 18 with a gap 34 therebetween, so that each delivery nozzle 17 can be moved inwardly toward each other during a casting campaign as explained below. It must be understood, however, that any suitable number of delivery nozzles 17 may be used, including two delivery nozzles 17 as described below and including any additional number of nozzles 17 disposed therebetween. For example, there may be a central nozzle segment adjacent to outer nozzle segments on either side.

Each delivery nozzle 17 may be formed in one piece or multiple pieces. As shown, each nozzle 17 includes an end wall 23 positioned nearest a confining side dam 20 as explained below. Each end wall 23 may be configured to achieve a particular desired molten metal flow in the triple point region between the casting rolls 12 and the respective side dam 20.

The side dams 20 may be made from a refractory material such as zirconia graphite, graphite alumina, boron nitride, boron nitride-zirconia, or other suitable composites. The side dams 20 have a face surface capable of physical contact with the casting rolls and molten metal in the casting pool.

A pair of carriage assemblies, generally indicated at 104, are provided to position the side dams 20 and the delivery nozzles 17. As illustrated, the twin roll caster is generally symmetrical, although such is not required. Referring to FIG. 5, one carriage assembly 104 is illustrated and described below, with the other carriage assembly 104 being generally similar. It is understood that the twin roll caster may utilize any number of carriage assemblies 104 configured in any suitable manner to provide a flow of molten metal to the casting pool 19. Each carriage assembly 104 is disposed at one end of the pair of casting rolls 12. Each carriage assembly 104 may be mounted fixed relative to the machine frame 10, or may be moveable axially toward and away from the casting rolls 12 to enable the spacing between the carriage assembly 104 and the casting rolls 12 to be adjusted. The carriage assemblies 104 may be preset in final position before a casting campaign to suit the width of the casting rolls 12 for the strip to be cast, or the position of the carriage assemblies 104 may be adjusted as desired during a casting campaign. The carriage assemblies 104 may be positioned one at each end of the roll assembly and moveable toward and away from one another to enable the spacing between them to be adjusted. The carriage assemblies 104 can be preset before a casting operation according to the width of the casting rolls and to allow quick roll changes for differing strip widths. The carriage assemblies 104 may be positioned so as to extend horizontally above the casting rolls with the nozzles 17 positioned beneath the distributor 16 in the casting position and at a central position to receive the molten metal.

For example the carriage assembly 104 may be positioned from tracks (not shown) on the machine frame 10, which may be mounted by clamps or any other suitable mechanism. Alternatively, the carriage assembly 104 may be supported by its own support structure relative to the casting rolls 12.

The carriage assembly 104 includes a support frame 125. A nozzle bridge 108 is moveably connected to the support frame 125 and engages the delivery nozzles 17 for selective movement thereof. A nozzle actuator 110 is mounted to the support frame 125 and connected to the nozzle bridge 108 for moving the nozzle bridge 108 and thus moving the delivery nozzles 17 to position the end wall 23 relative to the side dam 20. The nozzle actuator 110 is thus capable of positioning the delivery nozzles 17. The nozzle actuator 110 is a conventional servo mechanism. It must be understood, however, that the nozzle actuator 110 may be any drive mechanism suitable to move and adjust delivery nozzles 17. For example, the nozzle actuator 110 may be a screw jack drive operated by an electric motor, a hydraulic mechanism, a pneumatic mechanism, a gear mechanisms, a cog, a drive chain mechanism, a pulley and cable mechanism, a drive screw mechanism, a jack actuator, a rack and pinion mechanism, an electro-mechanical actuator, an electric motor, a linear actuator, a rotating actuator, or any other suitable device.

A nozzle position sensor 113 senses the position of the delivery nozzles 17. The nozzle position sensor 113 is a linear displacement sensor to measure the change in position of the nozzle bridge 108 relative to the support frame 125. The nozzle position sensor 113 may be any sensor suitable to indicate any parameter representative of a position of the delivery nozzles 17. For example, the nozzle position sensor 113 may be a linear variable displacement transformer to respond to the extension of the nozzle actuator 110 to provide signals indicative of movement of the delivery nozzles 17, or an optical imaging device for tracking the position of the delivery nozzles 17 or any other suitable device for determining the location of the delivery nozzles 17.

Each side dam 20 is mounted to a plate holder 100 which is moveably connected to the support frame 125 and engages the side dam 20 for selective movement thereof. A side dam actuator 102 is mounted to the support frame 125 and connected to the plate holder 100 for moving the plate holder 100 and thus moving each side dam 20 to position the side dam 20 relative to the casting rolls 12. The side dam actuator 102 is thus capable of positioning the side dam 20 and capable of cyclically varying the axial force of the side dams as described below. The side dam actuator 102 is a hydraulic force cylinder. It must be understood, however, that the side dam actuator 102 may be any suitable drive mechanism to position the plate holder 100 to bring the side dam 20 into engagement with the casting rolls 12 to confine the casting pool 19 formed on the casting surfaces 12A during a casting operation. Such a suitable drive mechanism, for example, may be a servo mechanism, a screw jack drive operated by electric motor, a pneumatic mechanism, a gear mechanisms, a cog, a drive chain mechanism, a pulley and cable mechanism, a drive screw mechanism, a jack actuator, a rack and pinion mechanism, an electro-mechanical actuator, an electric motor, a linear actuator, a rotating actuator, or any other suitable device. Thus, the side dams 20 are mounted in side dam plate holders 100, which are movable by side dam actuators 102, such as a servo mechanism, to bring the side dams 20 into engagement with the ends of the casting rolls. Additionally, the side dam actuators 102 are capable of positioning the side dams 20 during casting. The side dams 20 thus form end closures for the molten pool of metal on the casting rolls during the casting operation.

A side dam position sensor 112 senses the position of the side dam 20. The side dam position sensor 112 is a linear displacement sensor to measure the actual change in position of the plate holder 100 relative to the support frame 125. The side dam position sensor 112 may be any sensor suitable to indicate any parameter representative of a position of the side dam 20. For example, the side dam position sensor 112 may be a linear variable displacement transducer to respond to the extension of the side dam actuator 102 to provide signals indicative of position of the side dam 20, or an optical imaging device for tracking the position of the side dam 20 or any other suitable device for determining the location of the side dam 20. The side dam position sensor 112 may also or alternatively include a force sensor, or load cell for determining the force urging the side dam 20 against the casting rolls 12 and providing electrical signals indicative of the force urging the side dam against the casting rolls.

In any case the actuators 110 and 102 and the sensors 113 and 112 may be connected into a control system in the form of a circuit receiving control signals determined by measurement of the distance variation between the delivery nozzles 17 and the confining side dams 20, and between the side dams 20 and the casting rolls 12. For example, small water cooled video cameras may be installed on the nozzle bridge 108, or any other suitable structure, to directly observe the distance between the delivery nozzles 17 and the confining side dams 20 and the side dams 20 and the casting rolls 12, and to produce control signals to be fed to position encoders on the actuators 110 and 102. With any arrangement, precise control of the distance between the end walls 23 of the delivery nozzle 17 and the side dams 20 and the side dams 20 and the casting rolls 12 may be maintained. Moreover these distances can be accurately set and maintained by independent operation of the actuators 110 and 102 during casting. For example, the distance between the end wall 23 and the side dam 20 may be set so that a discharge of molten metal is positioned to a target area on the side dam 20 relative to the triple point regions.

During a casting campaign the control system of the twin roll caster is capable of actuating the side dam actuators 102 to vary the apply force on the side dams 20 against the ends of the casting rolls 12 in the axial direction, i.e. along the axis of the centerlines of the two casting rolls. The apply force is not varied such that the side dams 20 develop a clearance at edges of the casting rolls 12 that may cause leakage of molten metal from the casting pool. The control system may receive position or force information from the sensors 112 or from direct feedback of the actuator 102.

In accordance with an alternative embodiment of the present invention, a method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15% produced by continuous casting comprises: assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R_(′v)C_(rw)M_(x)B_(y)(P,C,Si)_(z), where R is one of iron, cobalt or nickel; R′ is one or two iron of iron, cobalt or nickel other than R; Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon; M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper; u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85, v=0-30, w=0-40, x=0-30, y=0-12, and z=0-7.5, with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent.

The molten metal thus delivered forms a casting pool of molten metal above the nip supported on the casting surfaces of the casting rolls. A heat flux in forming the thin strip on the casting rolls is provided with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls. A roll biasing force greater than 40 kN/meter of casting roll length is applied to form thin metal strip downwardly at the nip.

Once the strip exists the nip, the thin cast strip is conveyed through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% or 0.2% to form a thin steel strip. In one embodiment, the loop in the enclosure is between 2.8 and 3 meters. The cast strip is rolled through a rolling mill to impart between 10 and 40% reduction or heating the post cast strip to at least 70% of the melting point of the alloy forming the strip and initiating a modification of the microstructure of the cast strip to provide strip with of at least 900 MPa tensile strength and total elongation of at least 30%%, strip with tensile strength of at least 1200 MPa and total elongation of at least 20%, or strip with tensile strength of at least 1500 MPa and total elongation of at least 15%. The strip may have an unresolved microstructure at the surfaces, an equiaxed in the central portions, and columnar intermediate portions.

While the principle and mode of operation of this invention have been explained and illustrated with regard to particular embodiments, it must be understood, however, that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope 

What is claimed is:
 1. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%.
 2. The method of making steel strip as claimed in claim 1 where the loop in the enclosure is between 2.8 and 3 meters.
 3. A method of making alloy strip as claimed in claim 1 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 4. A method of making alloy strip as claimed in claim 1 where the casting rolls have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 5. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4%, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%.
 6. The method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% as claimed in claim 5 where the loop in the enclosure is between 2.8 and 3 meters.
 7. The method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% as claimed in claim 5 where the loop in the enclosure has a strain of not more than 0.2%.
 8. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% as claimed in claim 5 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions, and columnar intermediate portions.
 9. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% as claimed in claim 5 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 10. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel, R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%.
 11. The method of making alloy strip as claimed in claim 10 where the loop in the enclosure is between 2.8 and 3 meters.
 12. A method of making alloy strip as claimed in claim 10 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 13. A method of making alloy strip as claimed in claim 10 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 14. A method of making alloy strip with tensile strength of at least 900 MPa and total elongation of at least 30% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel, R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 900 MPa and total elongation of at least 30%.
 15. The method of making alloy strip as claimed in claim 14 where the loop in the enclosure is between 2.8 and 3 meters.
 16. The method of making alloy strip as claimed in claim 14 where the loop in the enclosure has a strain of not more than 0.2%.
 17. A method of making alloy strip as claimed in claim 14 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 18. A method of making alloy strip as claimed in claim 14 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 19. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 1200 MPa and total elongation of at least 20%.
 20. The method of making steel strip as claimed in claim 19 where the loop in the enclosure is between 2.8 and 3 meters.
 21. A method of making alloy strip as claimed in claim 19 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 22. A method of making alloy strip as claimed in claim 19 where the casting rolls have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 23. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4%, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 1200 MPa and total elongation of at least 20%.
 24. The method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% as claimed in claim 23 where the loop in the enclosure is between 2.8 and 3 meters.
 25. The method of making alloy strip as claimed in claim 23 where the loop in the enclosure has a strain of not more than 0.2%.
 26. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% as claimed in claim 23 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions, and columnar intermediate portions.
 27. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% as claimed in claim 23 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 28. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel, R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 1200 MPa and total elongation of at least 20%.
 29. The method of making alloy strip as claimed in claim 28 where the loop in the enclosure is between 2.8 and 3 meters.
 30. A method of making alloy strip as claimed in claim 28 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 31. A method of making alloy strip as claimed in claim 28 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 32. A method of making alloy strip with tensile strength of at least 1200 MPa and total elongation of at least 20% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel, R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 1200 MPa and total elongation of at least 20%.
 33. The method of making alloy strip as claimed in claim 32 where the loop in the enclosure is between 2.8 and 3 meters.
 34. The method of making alloy strip as claimed in claim 32 where the loop in the enclosure has a strain of not more than 0.2%.
 35. A method of making alloy strip as claimed in claim 32 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 36. A method of making alloy strip as claimed in claim 32 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 37. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.
 38. The method of making steel strip as claimed in claim 37 where the loop in the enclosure is between 2.8 and 3 meters.
 39. A method of making alloy strip as claimed in claim 37 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 40. A method of making alloy strip as claimed in claim 37 where the casting rolls have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 41. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition has a solidus temperature between 950 and 1200° C., a liquidus temperature between 1150 and 1350° C., and a freezing range between 100 and 250° C., (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4%, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.
 42. The method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% as claimed in claim 41 where the loop in the enclosure is between 2.8 and 3 meters.
 43. The method of making alloy strip as claimed in claim 41 where the loop in the enclosure has a strain of not more than 0.2%.
 44. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% as claimed in claim 41 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions, and columnar intermediate portions.
 45. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% as claimed in claim 41 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 46. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel, R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-45 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) rolling the cast strip through a rolling mill to impart between 10 and 40% reduction and initiating a modification of the microstructure of the cast strip to provide strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.
 47. The method of making alloy strip as claimed in claim 46 where the loop in the enclosure is between 2.8 and 3 meters.
 48. A method of making alloy strip as claimed in claim 46 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 49. A method of making alloy strip as claimed in claim 46 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width.
 50. A method of making alloy strip with tensile strength of at least 1500 MPa and total elongation of at least 15% produced by continuous casting comprising: (a) assembling a twin roll caster having a pair of counter-rotating casting rolls laterally positioned to provide a nip there between, (b) introducing molten metal to form a casting pool supported on the casting rolls above the nip and counter-rotating the casting rolls where the composition is of the formula: R_(u)R′_(v)Cr_(w)M_(x)B_(y)(P,C,Si)_(z), Where R is one of iron, cobalt or nickel R′ is one or two iron of iron, cobalt or nickel other than R, Cr, B, P, C, and Si respectively represent chromium, boron, phosphorus, carbon and silicon, M is one or more of molybdenum, vanadium, niobium, titanium, aluminum, tin, manganese and copper, u, v, w, x, y and z represent atom percent of R, R′, Cr, M, B and (P, C, Si), respectively, and having the following values: u=30-85 v=0-30 w=0-40 x=0-30 y=0-12 z=0-7.5 with the provisions that (1) the sum of v+w+x is at least 5, (2) when x is larger than 20, then w must be less than 20, (3) the amount of each of vanadium, manganese, copper, tin, magnesium may not exceed 10 atom percent, and (4) the combined amount of boron, phosphorus, carbon and silicon may not exceed about 13 atom percent. (c) providing a heat flux in forming the thin strip on the casting rolls with a peak heat flux of greater than 20 Mw/m² and heat flux after 25 milliseconds of greater than 8 Mw/m² to provide a weighted average heat flux of at least 10 Mw/m², and cooling the strip at 1000 to 3000 K/sec until the strip exits the nip between the casting rolls, (d) applying a roll biasing force greater than 40 kN/meter of casting roll length to form thin metal strip downwardly at the nip, (e) conveying the thin cast strip through a first enclosure with an atmosphere having an oxygen content of less than 5% immediately downstream of the casting rolls and on to a roller table while forming a loop of the cast strip with a strain of not more than 0.4% to form a thin steel strip, and (f) subjecting the cast strip to heating post casting to at least 70% of the alloy's melting point to modify the microstructure of the cast strip to provide strip with tensile strength of at least 1500 MPa and total elongation of at least 15%.
 51. The method of making alloy strip as claimed in claim 50 where the loop in the enclosure is between 2.8 and 3 meters.
 52. The method of making alloy strip as claimed in claim 50 where the loop in the enclosure has a strain of not more than 0.2%.
 53. A method of making alloy strip as claimed in claim 50 where the strip after step (c) has an unresolved microstructure at the surfaces, an equiaxed in the central portions and columnar intermediate portions.
 54. A method of making alloy strip as claimed in claim 50 where the casting roll have crown shape such that the cast strip within 25 millimeters of the edge of the strip have a higher temperature than the strip in the center portion of the strip width. 